Children exposed to “safe” levels of air pollution in the womb develop brain damage that impairs their concentration, a study has shown.

The research is the first to link common contaminants such as nitrogen dioxide and soot to changes in the brains of unborn babies that mean that they may later struggle to focus at school. The findings suggest that even comparatively clean city air could lead to worse academic performance and an increased risk of mental health problems such as addiction or attention deficit hyperactivity disorder.

In recent years scientists have found that children who grow up surrounded by air pollution are more likely to have a broad range of “neuro-developmental” difficulties, including autism and various kinds of cognitive impairment. However, only a handful